Samp were dealt another blow before the interval when defender Vasco Regini was sent off for a second bookable offence.

Palermo had chances to double their lead but failed to convert them and were ultimately punished with Gastaldello's last-gasp goal silencing the crowd at the Renzo Barbera stadium.

Last season's Serie B champions enjoyed a strong start and went ahead when Edgar Barreto found Dybala in the area and the South American coolly struck the ball from 12 yards past Sampdoria goalkeeper Emiliano Viviano.

Samp should have restored parity in the 21st minute but Pedro Obiang's goal-bound attempt was met by a fine save from Palermo goalkeeper Stefano Sorrentino.

Barreto almost doubled Palermo's lead on the half-hour mark but his bullet strike from 30 yards went wide of the far post.

Regini was then shown his second yellow card for a deliberate handball in the 41st minute, leaving his team to play on a man down.

Palermo dominated possession after the re-start but could not break Samp's well-placed defence until the 77th minute.

Andrea Belotti fed Franco Vazquez in the area and the striker fired way off target from a good position.

Samp had the last say of the game when Lorenzo De Silvestri headed a corner into the path of Gastaldello and the 31-year-old defender struck the ball from six yards past Sorrentino.